Characterization of breast tissues in density and effective atomic number basis via spectral x-ray computed tomography

Accuracy and consistency of effective atomic number over object size using deep silicon photon-counting detector CT

PURPOSE

Photon-counting detector (PCD) CT is the newest generation of CT detector technology. It is critical to characterize its performance in measuring important biomarkers used in quantitative CT including effective atomic number (Zeff). More accurate Zeff measurements could be beneficial in tissue classification and proton therapy tasks.

METHODS

A phantom of varying water-equivalent diameter (WED) containing clinically relevant inserts was scanned using a prototype deep silicon PCD CT and a dual-energy (DE) energy integrating detector (EID) CT. Zeff maps were generated. Measured Zeff values were compared across WEDs and to theoretical values.

RESULTS

The measured Zeff of the polystyrene, solid water, iodine, and bone (50% CaCO3) inserts differed from the theoretical value by a maximum of -14.0%, 4.6%, 8.4% and 13.0% respectively on EID vs 4.5%, 5.2%, 2.3% and 7.2% on PCD. The maximum variation in Zeff over the WED range on EID was 0.71, 0.27, 0.66, and 1.22 vs 0.47, 0.64, 0.1 and 0.22 on PCD for polystyrene, solid water, iodine, and bone (50% CaCO3) respectively.

CONCLUSION

This is the first study to evaluate Zeff measurements made using a prototype whole body PCD CT system. We found that PCD CT outperformed the EID CT in terms of Zeff accuracy and consistency over the WED range on most of the insert materials. Similarly, PCD CT outperformed most previous study's findings using EID CT. The high consistency and accuracy of measured Zeff using deep silicon PCD CT could make quantitative CT increasingly possible over a large range of patient sizes.

Evaluation of hafnium oxide nanoparticles imaging characteristics as a contrast agent in X-ray computed tomography

This research aimed to compare the quantitative imaging attributes of synthesized hafnium oxide nanoparticles (NPs) derived from UiO-66-NH2(Hf) and two gadolinium- and iodine-based clinical contrast agents (CAs) using cylindrical phantom. Aqueous solutions of the studied CAs, containing 2.5, 5, and 10 mg/mL of HfO2NPs, gadolinium, and iodine, were prepared. Constructed within a cylindrical phantom, 15 cc small tubes were filled with CAs. Maintaining constant mAs, the phantom underwent scanning at tube voltage variations from 80 to 140 kVp. The CT numbers were quantified in Hounsfield units (HU), and the contrast-to-noise ratios (CNR) were calculated within delineated regions of interest (ROI) for all CAs. The HfO2NPs at 140 kVp and concentration of 2.5 mg/ml exhibited 2.3- and 1.3-times higher CT numbers than iodine and gadolinium, respectively. Notably, gadolinium consistently displayed higher CT numbers than iodine across all exposure techniques and concentrations. At the highest tube potential, the maximum amount of the CAs CT numbers was attained, and at 140 kVp and concentration of 2.5 mg/ml of HfO2NPs the CNR surpassed iodine by 114%, and gadolinium by 30%, respectively. HfO2NPs, as a contrast agent, demonstrated superior image quality in terms of contrast and noise in comparison to iodine- and gadolinium-based contrast media, particularly at higher energies of X-ray in computed tomography. Thus, its utilization is highly recommended in CT.

A blurring correction method suitable to analyze quantitative x-ray images derived from energy-resolving photon counting detector

Objective.The purpose of this study is to propose a novel blurring correction method that enables accurate quantitative analysis of the object edge when using energy-resolving photon counting detectors (ERPCDs). Although the ERPCDs have the ability to generate various quantitative analysis techniques, such as the derivations of effective atomic number (Zeff) and bone mineral density values, at the object edge in these quantitative images, accurate quantitative information cannot be obtained. This is because image blurring prevents the gathering of accurate primary x-ray attenuation information.Approach.We developed the following procedure for blurring correction. A 5 × 5 pixels masking region was set as the processing area, and the pixels affected by blurring were extracted from the analysis of pixel value distribution. The blurred pixel values were then corrected to the proper values estimated by analyzing minimum and/or maximum values in the set mask area. The suitability of our correction method was verified by a simulation study and an experiment using a prototype ERPCD.Main results. WhenZeffimage of aluminum objects (Zeff= 13) were analyzed without applying our correction method, regardless of raw data or correction data applying a conventional edge enhancement method, the properZeffvalues could not be derived for the object edge. In contrast, when applying our correction method, 82% of pixels affected by blurring were corrected and the properZeffvalues were calculated for those pixels. As a result of investigating the applicability limits of our method through simulation, it was proven that it works effectively for objects with 4 × 4 pixels or more.Significance. Our method is effective in correcting image blurring when the quantitative image is calculated based on multiple images. It will become an in-demand technology for putting a quantitative diagnosis into actual medical examinations.